HOW DO THEY COMPARE

 

TABLE OF CONTENTS:

1. Equipment we use

2. Science of measuring headphones

3. Measurement process

4. Results

5. Using measurements

 

 Keep reading to unearth the process behind the comparison measurements. No time to read all now? Enter the email below, and we will email you a link to research later. No promotional emails, just science!

 

 

1. Equipment we use

First measurements of OLLO headphones were made using Mini DSP EARS measurement rig with a unique headphone compensation for a flat EQ target. In a quest to perfect our headphones, the development team needed something with better accuracy to test the new prototypes.

After thorough research and advice from Bang & Olufsen, we went for G.R.A.S 45CC using IEC 60318-1 ear simulator and Dewesoft AD conversion Sirius system. This is a gear used in top research labs like NASA, CERN, Mahle Sound and vibration labs, Spacelink, Airbus, SpaceX, Yamaha, and others.

HOW DO THEY COMPARE Grass 45 CC

More on the equipment we use here in this video: coming soon 

 

2. Science of measuring headphones

ANATOMY of THE BODY MATTERS - HRTF FUNCTION

Headphones can't be measured with standard measurement microphones. They have to be measured like they are used - coupled to a microphone that mimics the acoustic characteristics of the ear. So when we measure a headphone, we are trying to mimic what the eardrum hears.

Flat sound in the free field is not flat by the time it gets to your eardrum. This difference between the flat sound in the free field, and the EQ of the sound you hear at the eardrum when you stick your head in the sound in the free field, is called the Head Related Transfer Function.

HOW DO THEY COMPARE

Photo source: innerfidelity blog

Many things come into play that affects the EQ of the sound reaching your eardrum:

    • Your chest and head volume provide some acoustic gain at mid-frequencies.
    • Between 2000Hz and 5000Hz, the concha (the little cup in your outer ear around the entrance to your ear canal) acts as a focusing dish to get sound into your ear canals, and as a result, provides some significant gain to the signal at these frequencies.
    • The length of the ear canal provides the opportunity for modal artifacts, typically peaks at 3kHz, 9kHz, and 15kHz roughly, depending on the exact size and shape of the ear.

HOW DO THEY COMPARE Ear resonance

Photo source: innerfidelity blog

 

That's why when we measure headphones. We are not looking for a flat response. Instead, we are looking for a response that is altered in a way a flat response is altered in reality with the anatomy variables. A true flat is different for every individual. We tried to hit the perfect balance to deliver a flat response to as many engineers as possible.

Below is an example of Harman Target Curve on a raw measurement chart without any compensation. Dr. Sean Olive researched that in-depth and published quite some papers on the matter in AES Journals. His research empirically proved that the majority of consumers would enjoy about 5 dB boost in the low-frequency area. Our test with our endorsers shows that audio engineers prefer a bit less in the bass region due to clarity and masking effect that can quickly build up.

That's the basis for the frequency response design we undertook with the S4X headphones. You can see in the charts the low area is slightly elevated, but a bit less than Harman Target Curve suggests. The closest headphones to it that we got our hands on are AKG K371. Very nicely shown in graphs how their target curve is different than what we designed. Keep in mind the research was focused on finding out what consumers consider flat.

HOW DO THEY COMPARE Harman

 

 

More on Harman curve can be found in this great article on Innerfidelity pages: https://www.innerfidelity.com/content/first-test-estimated-harman-target-response-curve-various-headphones

 

FACT: OUR EARS HAVE an ABILITY to ADAPT

The Journal of Neuroscience published another interesting research on 28th March 2018. The hypothesis was that our spatial hearing depends on the shape of our ears, and once we learn how to interpret changes in frequency and amplitude of sounds, we would have problems adjusting our spatial positioning of sounds if your ears changed. In short, the research used test subjects and control subjects that were asked to locate a sound source around them. It was recorded that spatial localization from left to right (horizontal) was not affected much with rubber ear implants that changed the anatomy of the ear. On the flip side, vertical localization in the auditory cortex was very much changed. After a week of wearing implants, all test subjects learned the change in anatomy and correlated sound changes. Their brain takes over and learns to interpret the changed sound. Their spatial positioning was back to 100%.

This suggests that how we hear is different for everyone, but at the same time, our brain acts as a DAC with DSP if you will. This finding correlates to well-known advice from experienced audio engineers that you can use almost any monitoring system and learn to hear it flat. That also opens a question on how much is an acceptable tolerance or deviation of such system before simple physics of sound or mechanical vibrations start masking frequencies in harmonic ranges. Hence our brain could not do what they do in the absence of all that masked frequencies.

We tried finding proper research on this topic but was not able to find one just yet. For now, we can only put out an assumption that a double of SPL will start the masking effect. We hypothesize that a 3dB deviation in frequency response between harmonics is the limit. In short, if a system has a response of +3dB at 80Hz, it must not read 0dB or + 6dB at 160Hz. We'll continue to research this topic.

The basics were explained by many researchers on a topic of human hearing sensitivity in the free field, starting with well-known Fletcher and Munson curves from the early 20th century. It was standardized with ISO organization in 226 standard that tried achieving a useful standard for what is considered flat in everyday terminology by calculating the median of many researchers from a different time, universities, private labs, and test subjects from different global regions. What we know for a fact is that the attempt was good, and we do have a standard, but it still has massive tolerances in input data. For example, in the 200Hz area at 80phon, the tolerance is easily 10dB or more. This means the masking effect is in full swing.

Here's a plot of input tolerances we did based on data from the standard at 80 phons.

 

HOW DO THEY COMPARE Grass HPS S4

The ISO 226 standard and how the OLLO S4 curve fits its allowed tolerance.

What does it all mean?

It means that a flat line in the graph won't necessarily bring the best results. Some of our customers experienced this first hand when they tried to flatten the curve with the software for response flattening. They reported that the response curve looked more flat on the screen, but in reality, the results when mixing with such altered responses were not as good as with unaltered response. This is precisely the confusion that using standards create. The flat line on a screen is always based on some standard and compensation curves for headphones. It's based on some research that was not necessarily done empirically. In simple terms, no standard is an absolute truth. It's important, though, to have a response with acceptable tolerance or deviation that our ears can adapt to.

 

3. Measurement process

HOW DO THEY COMPARE Measurements

MEASURE MULTIPLE TIMES

Headphones must be measured in multiple positions to more accurately reflect the acoustic energy in the system. We took advice from Tyll Hertsens and move them, back, forward, up and down plus center position to average the results. How the sound hits the coupler, at what angle, and how tight the ear pads are will affect the measurement significantly.

The other problem is that the earphone coupler has internal dimensions that allow modal artifacts to appear. These are like the room modes you try to damp with acoustic treatments in your listening room but occur at much higher frequencies due to the small size of the chamber. These artifacts will move around as the size and shape of the enclosed volume changes with the position of the headphones on the ear. Therefore it is essential to carefully measure the headphones in several different positions to get an accurate idea of the acoustic energy being emitted from the drivers. This is called spatial averaging, as Tyll explains it.

POSITIONING THE HEADPHONES

Slight but realistic changes were made when positioning the headphones on the G.R.A.S 45CC  to see the difference the headphone position makes to a frequency response measurement. Pink noise was played over the headphones, and the measurements were compared with each other.  

MEASURING DATA

The headphones were all measured in a single day with the same equipment, one after the other, so there would be as little change of deviation as possible. Before every single headphone was measured, the loudness was set as close as possible to 80 dB at 600 Hz using pink noise as the source are reading it from the data acquisition system.

The reference environmental conditions were:
Static pressure: 100,3 kPa,
Relative humidity: 33%,
Temperature: 23°C.

List of headphones measures:

Headphone

Serial number

HPS S4

10300001

HPS S4R

20300002

HPS S4X

30300003

Sennheiser HD650

JX77MP

Sennheiser HD518

SN lost or not available.

AKG K371

MI4168-001160

AKG K712

058908

AUDIO-TECHNICA ATH-M50X

1750

AUDEZE LCD-1

L1200842

Beyerdynamic DT 770 PRO

SN lost or not available.

Beyerdynamic DT 990 PRO

SN lost or not available.

SHURE SRH1440

AB961F


COMPARE COMPARABLE 

To sum up - there are different variables one has to take into account when measuring the headphones so that the curves can be compared. That's why comparing measurements from different labs, or even reviewers can be very misleading. Make sure you have the measurements normalized, and you know for a fact what you're comparing goes together. Compare only one standard and do not do cross-comparisons!

HOW DO THEY COMPARE Grass 45 CC

4. Results

FREQUENCY RESPONSE CURVES

 

5. Using measurements

GET YOUR INDIVIDUAL MEASUREMENTS

Each OLLO headphone comes with an individual frequency response measurement graph in the box when you buy them.

HOW DO THEY COMPARE MeasurementsHere is how you get your OLLO headphones measurements data if you bought them before April 2020:

  1. Create an account here on the website: https://olloaudio.com/account/register

    PLEASE NOTICE! With our newest website migration, all the accounts made before December 2019 were deleted according to GDPR laws, and you'll have to register again. We apologize for the inconvenience caused. 

  2. When in your account, click on the "get measurements" link that will take you to our Google Drive

  3. Find your serial number (it's written in your manual and on the printed version of the graph) then download the file.

  4. Return to our website and click on "get REW software" to install the free software that will open the measurements.

Here is how you get your OLLO headphones measurements data if you bought them after April 2020:

  1. Please write us an email that contains your serial number. An excel file will be sent to you, which will provide data for your specific headphone.

 

 

WORKING WITH MEASUREMENTS

  1. Adjusting the scale

Once you have your measurements opened in REW software, the first thing is to adjust the scale of the graph to a resolution that can provide you with some insightful data. In a too broad scale, your response will be just a flat line, that doesn't tell you anything. Zooming in too much will reveal all the little deviations from 0dB, but you can’t really use that as those differences are so small your ears won't even perceive them, and there is no need to complicate your life by compensating for them.

HOW DO THEY COMPARE Scale

Every headphone has some deviations from 0. You need to be able to see that deviations in parameters that help you do something with them.

10 dB scale is something that, in our opinion, represents how headphones sound the best and offer the most useful view to benefit from when trying to improve the overall response.

2. Identify the room for improvement.

Find deeps and boosts in the curve that is greater than 3dB. Find the center of the plot. Doing that with your eyes is accurate enough, no need to go crazy with a ruler. :)

4. Go to your EQ and mimic the situation, just in reverse.

So if your measurements have a boost with the highest point on 200 Hz, you should set the EQ to that frequency and cut it down a half step. If it’s a 4 dB boost, you cut it down 2 dB. Also, try using low Q factors below 1. High Q factors will cause more phase issues than anything else. We are intentionally using half measures because of the way speakers acoustics responds to the input signals. If we take the low frequency with a lot of energy out, that would also affect how much harmonics we have left, how much room it's going to be in the ear cup for other frequencies to develop. Do this with all the significant bumps and boosts. Probably 2-3 areas on most headphones.

 The whole process is described in the video below:

 

 

6. YOUR EARS ARE THE BEST JUDGE.

We know it's challenging to make an educated decision based on tech specs and reviews. The only true way to know if it's for you is to try it out. That's why we offer a 30 days trial period. If the headphones don't suit you, just send them back, and we will refund your purchase, no questions asked.

 

S4X REFERENCE

Flat out of the box.
Neutral and brutally honest.

399,00€
In preorder: 289,80 €

PREORDER NOW

 

Sources for further research:

Innerfidelity blog https://www.innerfidelity.com/

The Journal of Neuroscience https://www.jneurosci.org/content/38/13/3252

AES Journal: http://www.aes.org/journal/